The invention relates to a method and an apparatus for dismantling a stack of flat objects piece by piece.
A method and an apparatus of the described type are disclosed by CH 436349. In the method described there, a stack of flat objects is dismantled piece by piece by the top object on the stack being rotated out of the stack in its plane, gripped at its freed edge and removed from the stack. The top object is moved with a drive element or separating element which, on the top object, can be switched toward and away from the latter. In order to grip and remove the object rotated out, conveying means are used. The known method has the advantage that the movement of the top object in its plane can be implemented very simply. However, the friction between two objects resting on one another is a problem in this case, and leads to the second object from the top being carried along during the movement of the top object. As a result, gripping the top object rotated out is made more difficult, and the alignment of the stack is disrupted.
A further apparatus for separating and conveying sheets is disclosed by DE-A 4136194. In this case, the top sheet is accelerated obliquely with respect to the sheet leading edge and gripped at a freed edge. Here, too, there is the problem that sheets lying further down are carried along by friction during the movement of the top sheet.
A further apparatus, in which individual sheets of a sheet stack are separated by being rotated by means of a turntable, is disclosed by DE-A 19642485. In order to prevent the lower sheets from slipping during the rotation of the top sheet, corner separators are fitted at at least three corners of the sheet stack. These have the task of holding on the stack at least the sheets lying in the upper region of the sheet stack. In order to further prevent slipping, it is proposed to place a clamping finger on the free surface, which is produced during the rotation of the top sheet, of the sheet lying in the second from top position. The clamping finger is able to act on this free surface and hold the sheet stack. Both solution proposals have the disadvantage that the position of the corner separators or the clamping finger have to be matched to the instantaneous stack height. The height of the corner separators has to be chosen such that the three corners of the top sheet can move over the corner separators, but the sheets lying underneath are not rotated at the same time. The clamping finger has to be controlled synchronously with the rotation of the top sheet in such a way that it always firmly holds the second sheet from the top and releases it at the correct time. The cycle rate of the apparatus is limited, since the top sheet must first be conveyed out of the stack to a great extent before the turntable can make access to the second sheet from the top.
The invention is therefore based on the object of specifying a method and an apparatus in which the individual objects can be removed from a stack in a straightforward way at a high cycle rate, without impairing the stack formation. The removal of the top object is to proceed independently of the stack height.
The above and other objects and advantages of the present invention are achieved by the provision of a method and apparatus which are particularly suitable for separating very flat, flexible objects such as paper or plastic sheets. According to the invention, the top sheet is moved in its plane against a stop, at least in the region of one of its corners by a movable separating element. Because it strikes the stop, and in the process continues to be moved, it is bent in such a way that it escapes from the stop, preferably sideways, and is moved out of the stack. All the objects lying under the top object are stopped by the stop and remain aligned if they were moved together with the top object in a frictional connection.
The top object is preferably moved with a movement component perpendicular to the stop and a movement component transversely thereto, so that it strikes the stop, is compressed against the latter and finally jumps away from the latter transversely and can preferably be moved onward in its plane, for example also by suitable output conveying means. The stop preferably acts only on one corner of the object. Such a stop can easily be overcome by the top object, while it reliably holds all the other objects of the stack in position. The stop preferably extends from the supporting surface of the stack up to a height which is slightly greater than the typical stack height. The height of the stop does not have to be matched to the stack height, in particular if the top object, as already described, is pushed past the stop sideways.
The top sheet can be moved linearly, in the case of a rectangular object preferably obliquely with respect to its edges and to the alignment of the stop. However, a rotational movement of the top object can be implemented particularly simply about an axis of rotation running perpendicular to the plane of the object. The top object is set moving by a separating element which preferably acts on the top object with a forcible or frictional connection. A separating element with a suction action can also be used. Furthermore, the trailing edge of the object can be lifted by a sucker and a slider, which slides the object out of the stack, and can engage under it.
Because the separating element is movable, an increase in the cycle rate is possible. The top sheet is moved by the movement of the separating element in a forcible or frictional connection until it jumps off the stop and is offset with respect to the stack surface. The separating element is then moved back into its initial position, where it makes immediate access to a region of the second sheet from the top which is now exposed and can move said sheet during the renewed forward movement. During this time, the top sheet is drawn out of the stack by suitable output conveying means. xe2x80x9cGrippingxe2x80x9d is understood to mean any type of transfer to the output conveying means, for example, also by being deposited on a conveyor belt. By means of the invention, an overlapping formation of the separated sheets can be produced particularly simply. The separating element preferably describes part of a circular path. The stroke or the distance covered needs to be only sufficiently long for the edge of the top sheet moved against the stop to jump off the stop. Depending on the configuration of the stop, therefore, a movement path of fractions of the sheet length is sufficient. The cycle frequency of the apparatus can be increased accordingly.